1. Field of Invention
The present invention relates to electronic frequency conversion of the power output of generators.
2. Description of Prior Art
Prior art frequency converters, such as the circuits of U.S. Pat. Nos. 3,089,992; 3,493,843 and 3,593,104, have been attempts to control the frequency of electric power from a generator or power source to a suitable frequency which was within the operating frequency limits of the load being driven. The inductive loads of these converters have posed problems due to "flyback" voltages when current flow in these inductive elements was interrupted or terminated.
These prior art attempts have, so far as is known, typically rectified the higher frequency generator output in one or more full-wave rectifier bridges in complicated circuitry to form groups of unidirectional pulses which were gated from the rectifiers to the load or loads through electronic switching circuits, such as silicon-controlled rectifiers (SCR's), which in operation exhibited erratic switching characteristics unless timing precautions were taken. For example, in attempting to turn-off an SCR by bringing anode and cathode potential to zero volts, such potential had to remain at zero for a given length of time known as "turn-off" time. With full-wave rectification, however, only an instantaneous voltage level of zero was present before voltage levels swung positive again.
In the circuit of U.S. Pat. No. 3,089,992, an expensive precision-controlled oscillator was used to achieve precise timing control of switching to transfer power from full-wave rectifiers at a desired frequency, attempting to prevent a timing imbalance of the times of negative and positive polarity output from the converter which would present an undesirable direct current flow in inductive elements. The circuit of U.S. Pat. No. 3,593,104 was intended for conversion of frequencies ranging from within a suitable range for the load to greatly in excess of the suitable range, and thus involved relatively complex circuitry because of the frequency range.
In the frequency converter circuit in U.S. Pat. No. 3,493,843, inhibiting circuitry rendered two full-wave, gatecontrolled rectifier bridges inoperative for one-half cycle of the input frequency when power connections to the bridges were being changed after a predetermined count of input frequency half-cycles.